5 lectures + background reading (Campbell) Cell structure (chapter 7) Cell membranes (chapter 8) Cell division (chapter 12) Respiration (chapter 10) Photosynthesis (chapter 11)
Crucial structures of cells Makes a cell a cell! Also called a plasma membrane Fluid mosaics of lipids and proteins Most abundant lipids are phospholipids
Phospholipids have hydrophilic heads and hydrophobic tails Forms a stable two layer membrane between aqueous compartments The hydrophobic tails are “shielded” from the water
Membranes are dynamic! Phospholipids switch places laterally 10 million times per second Some proteins also move around (others attached to plasma membrane) Fluidity changes with temperature
Determine most of the membrane function Can be: Integral, embedded in the membrane (including transmembrane) Peripheral, loosely bound to membrane surface
Diagram shows transmembrane protein Internal hydrophobic region, contains α helices Hydrophilic regions either side of membrane Can be held in place by cytoskeleton
Membranes are selectively permeable Constant flow of molecules and ions Examples: In: nutrients, O2, inorganic ions Out: waste, CO2, inorganic ions Molecules passively move through lipid bilayer with varying difficulty Membrane proteins also allow specific molecules to pass through
Solutes diffuse across membranes when there is a difference in concentration This requires no energy Move towards equilibrium (equal) concentration either side of membrane E.g. O2 transport into cells
Membranes that are selectively permeable produce interesting effects If a solute cannot move along a concentration gradient, water moves instead Water exchange allows equilibrium BUT water balance is extremely important for cells!